Zimbabwe Sugarcane Irrigation

Optimizing Field Layout, Field Topography & Furrow Irrigation

Location: Zimbabwe, Africa
Field Area: 136 acres or 55 hectares
Irrigation Method: furrow irrigation
Crops: sugarcane

The client was looking to apply furrow irrigation to a new 250ha (625 acre) area. Layflat or flume piping was to be used to supply water to each furrow.

This case study focuses on the the northern 55ha field but the whole area was designed together to ensure efficient layout.

Figure 1. Proposed Topography Overlaid in Google Earth.

Field Layout Design

The first step was the fields layout design. The main considerations for this was to optimize the field shape and furrow direction to promote rows lengths and headland angles for more efficient mechanized farming and irrigation while restricting required earthwork to achieve this.

In addition to furrow direction, the main design variable came down to optimizing the placement of the tail drain alignment and parallel head land beside it (for next field down) to achieve consistent slope for the drain and the layflat pipe with acceptable earthworks. The optimised taildrain/headland alignment achieved an average slope of 0.1% which suits the drainage and layflat pipe nicely.

OptiSurface Designer's Drainage Analysis Tool can be used to test different furrow directions and field boundaries quickly to see the proportion of the field that would have drainage problems (standing water) and therefore need earthworks to rectify. The figure below shows the original topography and where water would pond if no earthworks work done with the final field layout and furrow direction selected (drag the slider). The areas with drainage problems are minimal indicating a good field layout design.

Figure 4. Existing Topography (left) and Drainage Analysis (right). Drag the slider left or right to view each.

Also note the field has considerable natural slope of up to 0.6%. Rotating the row direction around to be slightly across the natural slope allowed the furrow slope to be reduced to promote better furrow irrigation and reduce erosion risk.

Field Landform Design

The next step was the landform design of the field to ensure good surface drainage and promote more uniform furrow irrigation. The main slopes were set to 0.20% to 0.50% and the smoothing was at 100 m/%.

Figure 5. Existing Topography (left) and Proposed Topography (right). Drag the slider left or right to view each.

Figure 6 shows the Cut/Fill Map with only 97 m3/ha of earthworks.

Figure 6. Proposed Cut/Fill Map.

Furrow Irrigation Optimization

Finally, the furrow irrigation was optimized using the OptiIrrigate tool based on irrigation time, target irrigation depth and other parameters as shown in Figure 7.

The Water Values are what we use to optimize on.  We're trying to optimize the 'Irrigation Gross Margin' which are the inflow cost, root zone value, deep drainage value and runoff value.

Figure 7. Irrigation Analysis parameters.

The resulting maps are Infiltration Depth, Optimal Irrigation Cut-off Time and Optimal Irrigation Inflow Rate.

Figure 8. Irrigation Infiltration Depth Map.

Table 1. Furrow Irrigation Optimization Results

The Profile of the Infiltration Depth Map is shown in Figure 9. The blue line is the infiltrated depth and the the orange line is the target depth of 70mm (figures are multiplied by 10 just to show the difference).

As you can see we're pretty right on 70mm, just over a touch. As we get to the end of the field we get less and a bit under the target irrigation depth as expected.

Figure 9. Irrigation Infiltration Depth Profile.

The optimized inflow rate is shown for all furrows across the field in Figure 10. It ranges from 2.75 L/s in the shorter furrows (about 350m long) to around 4.1L/s for the longer furrows (about 700m long). This difference in optimal flow is mainly due to the furrow length difference not slope as most people think.

Figure 10. Optimum Furrow Inflow Rates

The video below shows Graeme discussing how the Furrow Irrigation Analysis tool was used for the field.

No other software gives you the ease and flexibility of optimizing irrigation like this. OptiSurface lets user design a field and simulate irrigation on the proposed design to maximize efficiency.

Conclusion

Figure 11. Satellite image of the area before lanforming (left) and after landforming (right). Drag the slider left or right to view each.

The client was very happy how the project turned out and applied the same to the rest of their farming operations.

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